/Engine/Source/Runtime/CoreUObject/Public/UObject/WeakObjectPtr.h
Weak object pointer serialization. Weak object pointers only have weak references to objects and won't serialize the object when gathering references for garbage collection. So in many cases, you don't need to bother serializing weak object pointers. However, serialization is required if you want to load and save your object.
void Serialize ( [FArchive](API\Runtime\Core\Serialization\FArchive) & Ar )